Electrochemical and x-ray diffraction measurements have been performed on two lithium deficient lithium manganese oxide phases, namely Li0.16Mn2O4 and Li0.08Mn2O4. These materials were prepared by a chemical oxidative treatment of the parent LiMn2O4 spinel phase in acidic conditions. The results are compared and contrasted with equivalent measurements carried out on the parent spinel phase. The lithium deficient materials show a characteristic featureless voltage curve during the initial lithium intercalation process quite unlike that in the parent compound LiMn2O4. The results presented highlight a distinct difference in the initial electrochemical behavior of chemically and electrochemically de-lithiated LiMn2O4. Following the initial lithium intercalation process the materials’ electrochemical performance appear to revert to those of the parent spinel compound. The excellent electrochemical reversibility of the lithium insertion/extraction reactions in these phases is demonstrated conclusively.